THE OBJECTIVES OF THIS WORK ARE: 1) to determine whether terminal deoxynucleotidyl transferase is of actual clinical value in the diagnosis, treatment and prognostication of patients with acute lymphoblastic leukemia; 2) to prepare antibodies against terminal deoxynucleotidyl transferase from human cells so that these antibodies could be used to develop a immunofluorescent test for this enzyme which may prove useful for the detection of leukemic lymphoblasts.